Color filters used in display panels typically include a matrix comprising a plurality of color features. The color features may include patterns of red, green and/or blue color features, for example. Color filters may be made with color features of other colors. The color features may be arranged in any of various suitable configurations. Prior art stripe configurations have alternating columns of red, green and blue color features as shown in FIG. 1A.
FIG. 1A shows a portion of a prior art “stripe configuration” color filter 10 having a plurality of red, green and blue color features 12, 14 and 16 respectively formed in alternating columns across a media or receiver element 18. Color features 12, 14 and 16 are outlined by portions of a matrix 20. The columns can be imaged in elongate stripes that are subdivided by matrix cells 34 (herein referred to as cells 34) into individual color features 12, 14 and 16. TFT transistors on the associated LCD panel (not shown) may be masked by areas 22 of matrix 20.
Laser-induced thermal transfer processes have been proposed for use in the fabrication of displays, and in particular color filters. When laser-induced thermal transfer processes are used to produce a color filter, a color filter substrate also known as a receiver element is overlaid with a donor element that is then image-wise exposed to selectively transfer a colorant from the donor element to the receiver element. Preferred exposure methods use radiation beams such as laser beams to induce the transfer of the colorant to the receiver element. Diode lasers are particularly preferred for their ease of modulation, low cost and small size.
Laser induced “thermal transfer” processes include: laser induced “dye transfer” processes, laser-induced “melt transfer” processes, laser-induced “ablation transfer” processes, and laser-induced “mass transfer” processes. Colorants transferred during laser-induced thermal transfer processes include suitable dye-based or pigment-based compositions. Additional elements such as one or more binders may be transferred, as is known in the art.
Some conventional laser imaging systems have employed a limited number of imaging beams. Other conventional systems have employed hundreds of individually-modulated beams in parallel to reduce the time taken to complete images. Imaging heads with large numbers of such “channels” are readily available. For example, a SQUAREspot® model thermal imaging head manufactured by Kodak Graphic Communications Canada Company, British Columbia, Canada has several hundred independent channels. Each channel can have power in excess of 25 mW. The array of imaging channels can be controlled to write an image in a series of image swaths which are closely abutted to form a continuous image.
The stripe configuration shown if FIG. 1A illustrates one example configuration of color filter features. Color filters may have other configurations. Mosaic configurations have the color features that alternate in both directions (e.g. along columns and rows) such that each color feature resembles an “island”. Delta configurations (not-shown) have groups of red, green and blue color features arranged in a triangular relationship to each other. Mosaic and delta configurations are examples of “island” configurations. FIG. 1B shows a portion of a prior art color filter 10 arranged in a mosaic configuration in which color features 12, 14 and 16 are arranged in columns and alternate both across and along the columns. Other color filter configurations are also known in the art.
Each of color features 12, 14 and 16 may overlap adjoining portions of matrix 20. Overlapping matrix 20 with the color features can reduce leakage of backlight between the features. FIG. 1C schematically shows a conventional stripe configuration color filer in which the color features 12, 14 and 16 are formed from color stripes that fully overlap portions of matrix 20 along columns of the filter but partially overlap matrix 20 along the rows of the filter. FIG. 1D schematically shows a conventional mosaic configuration color filter in which each of the color features 12, 14 and 16 are islands that each partially overlap matrix 20 across both the rows and columns of the filter. In applications like color filters, the visual quality of the final product is dependant upon how accurately a repeating pattern of features (e.g. the pattern of color filter features) is registered with a repeating pattern of registration sub-regions (e.g. matrix). Misregistration can lead to the formation of undesired colorless voids and/or the overlapping of adjacent color features which can form an undesired color combination.
Overlapping a matrix may help to reduce the precision with which the color features must be registered with matrix. However, there typically are limits to the extent that a matrix can be overlapped. Factors that can limit the degree of overlap (and final registration) can include, but are not limited to: the particular configuration of the color filter, the width of the matrix lines, the roughness of the of the matrix lines, the minimum overlap required to prevent light back leakage, and post annealing color features shrinkage.
Factors associated with the particular method employed to produce the features can limit the degree of overlap. For example, when laser imaging methods are employed, the precision with which the laser imager can scan the color filter will be applicable to the final registration obtained. The addressability associated with the imaging channels of the imaging head defines the resolution with which the features can be imaged also has a bearing on the final registration. The orientation of the color filter with respect to a scan path of the imaging head can also have a bearing on the registration.
The laser imaging process employed can also have an effect on the degree of overlap that is permitted. For example, the visual quality of an image produced in a laser-induced thermal transfer process is typically sensitive to the amount of image forming material that is transferred from a donor element to a receiver element. The amount of transferred image forming material is typically sensitive to the spacing between the donor element and receiver element. If adjacent features of different colors overlap themselves over portions of the matrix, the donor-to-receiver element spacing will additionally vary during the subsequent imaging of additional donors elements, possibly impacting the visual quality of the features imaged with these additional donor elements. In this regard, it is preferred that adjacent features of different colors not overlap themselves over a matrix portion. This requirement places additional registration constraints on the required registration between the pattern of repeating color features and the repeating pattern of matrix cells.
To increase production throughput, a plurality of color filter displays is usually formed on a universal receiver element 18 and which is subsequently imaged with different color donor elements using laser-induced thermal transfer techniques to image the plurality of displays. Post-imaging, the universal receiver element 18 is separated to form the individual color filter displays. Although a matrix 20 can be produced on a receiver element 18 by laser-induced thermal transfer techniques, matrix 20 is typically produced by standard photolithographic methods. Photolithographic techniques typically employ an exposure apparatus to illuminate a mask to form a pattern on a substrate. Upon exposure the pattern is developed and a medium is transferred to the substrate via the pattern to form various entities such as matrix 20.
However, photolithographic techniques can become expensive when large universal substrates are exposed since both larger exposure units and masks are needed. To help mitigate these additional costs, smaller masks are employed with step and repeat exposure apparatus. A plurality of smaller masks are superposed over the substrate and imaged in a step and repeat fashion with smaller exposure units. Although these techniques may reduce the costs of forming multiple matrixes on a single universal substrate, additional problems may arise during the subsequent formation of the color features. For instance, the use of a plurality of masks may lead to varying degrees of misregistration between the multiple back matrixes that are formed. Misregistration between multiple matrixes create additional challenges in terms of accurately imaging a plurality of repeating color feature patterns in correct registration with their corresponding matrixes disposed on a universal receiver element.
There remains a need for effective and practical imaging methods and systems that permit the making of a plurality of high-quality images of repeating patterns of features, such as the patterns of color features in a color filter on a universal substrate.
There remains a need for imaging methods and systems that permit the making of a repeating patterns of features (e.g. the patterns of color features in a color filter), in register with a repeating pattern of registration sub-regions (e.g. the pattern of cells in a matrix).